Unequal Pupils (anisocoria) in Cats
Key takeaways
Unequal pupils, or anisocoria, is a rare symptom in cats that describes when the pupil of one eye is not the same size as the other.
- Anisocoria results from either dilation or constriction of one pupil independently of the other
- Unequal pupils can occur as a result of various conditions (e.g., injury, infections, cancer, central nervous system (CNS) abnormalities, and eye inflammation), some of which can be life-threatening; as such, veterinary attention is always advised
- Cats with anisocoria may undergo a number of diagnostics to identify the underlying cause, including blood and urine tests, neurological examinations, diagnostic imaging, and specific ophthalmic tests
- Treatment and prognosis are extremely variable as they depend on the underlying condition
- Treatment options vary from outpatient, non-medical care to surgery
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A closer look: Unequal Pupils (anisocoria) in Cats
Anisocoria is not a life-threatening symptom in and of itself, but can be a sign of a severe underlying condition. As such, prompt medical attention is advised.
Anisocoria is uncommon in cats. Unlike dogs, cats very rarely suffer from short-term idiopathic anisocoria; the presence of anisocoria is considered an indicator of an underlying condition in cats.
Some cases of anisocoria may be accompanied by vision loss. Any sudden-onset of vision loss is a medical emergency. Immediate veterinary attention provides the best chance of preserving vision.
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Possible causes
Horner syndrome is commonly associated with anisocoria; the condition presents as the combination of five distinct symptoms in the affected eye.
Risk factors
Pupils can be affected by one of two opposite conditions, unilateral miosis (constriction of the pupil) or unilateral mydriasis (dilatation of the pupil). The degree of dilation or constriction of the pupils can also vary. Depending on the underlying cause and several other variables (e.g., the lighting in the room, the alertness/excitement of the pet), the symptom may also be more, or less obvious.
In many cases anisocoria is a minor secondary symptom of an underlying condition, and rarely causes any pain or discomfort.
Testing and diagnosis
Anisocoria is an easily recognizable symptom by both veterinarians and pet parents. Further diagnostic tools are necessary to determine the underlying conditions causing the symptom; they include:
- Blood work
- Urinalysis
- Ophthalmic examination
- Neurological exams
- Diagnostic imaging (X-rays, ultrasound of the eye)
- Electroretinography (measures electrical activity of the eye)
Referral to a specialist may be required.
Treatment of the underlying cause varies greatly. Treatment options include, but are not limited to:
- Medication (e.g., antibiotics, anti-inflammatories)
- Supportive care (e.g., intravenous fluids, cage rest)
- Surgery
Similar symptoms
Anisocoria is self-evident and not likely to be confused with other symptoms.
Associated symptoms
Cats presenting anisocoria are likely to present with a number of other symptoms.
